The present invention relates to a method for manufacturing a ceramic substrate.
A low-temperature-sintered ceramic (LTC) substrate among multi-layer ceramic circuit substrates is recently used for down-sized components in electronic appliances such as personal computers or cellular phones. This type of the multi-layer ceramic circuit substrate is formed by a method in which ceramic green sheets (GS""s) which is not sintered are stacked, i.e., a GS stacking method. As a method of forming conductive patterns, a screen printing method is generally applied for forming internal interconnections. A screen printing method, thin film photolithography or thick film photolithography is generally known for forming surface electrical connections on ceramic substrates.
Appliances such as cellular phones require down-sized, light electronic components. An LCR hybrid circuit substrate which forms a filter including inductors, capacitors, and resistors incorporated in a multi-layer ceramic substrate thereof is developed as a printed circuit board. A fine line pattern technology is required because the elements such as LCR and internal conductive patterns are formed by a screen printing method.
A current screen printing method, however, can provide a line pitch (wire diameter+clearance) of 100 xcexcm at the narrowest at a mass-production stage.
A conventional method for manufacturing multi-layer ceramic circuit substrates formed with green sheets will be described with referring to FIG. 9. At step 9a, through-holes 92 are punched in an un-sintered ceramic green sheet 91 with a puncher, piercing die or YAG laser apparatus or the like. At step 9b, the through-holes 92 of the green sheet 91 are filled with conductive paste, and via-hole conductors 93 are then formed by a screen printing method or the like with metal screen plates. At step 9c, conductive patterns 94 are formed on the green sheet 91 with conductive paste by a screen printing method. At step 9d, plural green sheets 91 are stacked and heat-pressed, thus being integrated. At step 9e, a de-binder process for removing a binder and a sintering process are applied to the stacked assembly. Then, the green sheet 91 becomes a sintered ceramic substrate 95, and the via conductors 93 and conductive patterns 94 become sintered via conductors 96 and sintered conductive patterns 97, respectively. The conductive pattern has a thickness ranging approximately 7 to 8 xcexcm.
The conventional screen printing method can provide a pitch of 100 xcexcm at the narrowest in internal conductive patterns
As a method for forming high-density conductive patterns on ceramic substrates, a film-intaglio-transfer-printing method is well known. The printing method provides both very fine line patterns (approximately 40 xcexcm pitch between wires) and a high aspect ratio (approximately 10 xcexcm thickness after the sintering). The film-intaglio-transfer-printing method can be applied to manufacturing ceramic circuit substrates in two manners.
In one manner, a multi-layer ceramic circuit substrate is manufactured by stacking the GS""s having conductive patterns formed by the film-intaglio-transfer-printing method. In the other manner, the multi-layer ceramic circuit substrate is manufactured by stacking sintered ceramic substrates having conductive patterns formed by the film-intaglio-transfer-printing method and un-sintered green sheets alternatively.
When, however, the conductive patterns are transfer-printed directly onto the GS""s by the film-intaglio-transfer-printing method, a surfaces of the GS""s are necessarily coated with an adhesive layer composed mainly of thermoplastic resin. However, the GS""s can not be coated with the adhesive layer because an organic solvent dissolves the adhesive layer. In addition to this, the un-sintered green sheets and sintered ceramic substrates, upon being stacked alternatively, may hardly be adhered with each other, and thus, may be de-stacked between the sheets during being heat-pressed, having the binder removed, or being sintered.
A method of manufacturing a ceramic circuit substrate having a fine conductive pattern as an internal conductive pattern formed by a film-intaglio-transfer-printing method is provided.
The manufacturing method includes the following steps:
(a) Filling an intaglio with a conductive paste to form the conductive pattern by the film-intaglio-transfer-printing method;
(b) Forming an adhesive layer on a heat-resistant substrate;
(c) Heat-pressing the intaglio on the adhesive layer
(d) Removing the intaglio; and
(e) Forming an assembly through heat-pressing an un-sintered green sheets covering the conductive pattern. The assembly has a binder removed and is sintered, and thus, provides a ceramic substrate.